The invention is based on a fuel injection apparatus for internal combustion engines including a mechanically driven pump piston of an injection pump, a pump work chamber in the pump, a control slide limited by a pressure chamber and actuatable by control pressure of a source of control fuel common to all pumps counter to the force of at least one restoring spring, the control slide being located in a discharge channel in communication with the pump work chamber and arranged to close the discharge channel at will to initiate the variable onset of injection, and to open the channel again to terminate the injection, and a control apparatus for exerting pressure via the control lines on the pressure chambers of the control slides. A fuel injection apparatus of this type is already known (U.S. Pat. No. 3,486,493) in which the injection pump is embodied as a pump/nozzle, and the fuel injection quantity is determined by a hydraulically driven control slide inserted into an overflow channel. This control slide determines the effective supply stroke, and thus the fuel injection quantity of the injection pump, by means of blocking the return flow of fuel out of the pump work chamber; and the injection is terminated whenever this control slide opens the overflow channel and the injection pressure can be relieved. In the known apparatus, the control slide is exposed to the supply pressure of the supply pump, and it is actuated by means of pressure relief in its spring chamber containing the restoring spring. In order to initiate the onset of injection, it is thus only the actuation force resulting from the supply pressure minus the force of the restoring spring that is available; and in order to terminate the injection, only the force of the restoring spring is available, because both end faces of the control slide are placed under identical pressure at the end of injection. This restricts the applicability of such an apparatus in high-speed engines. A further disadvantage is that the control pressure line also acts as a filling line, so that retroactive influences on the control must be expected.
A fuel injection apparatus of virtually the same type is known from U.S. Pat. No. 3,465,737; however, in this apparatus the control slide is actuated by the control pressure of a separate injection pump, which acts as the control pump and is driven simultaneously with the pump/nozzle unit. In order to vary the onset of injection, a known injection adjuster which transmits the drive torque is built into the drive mechanism of the control pump, so the total expenditure for the apparatus is very high. It is the object of the invention to obtain a compact injection apparatus at low manufacturing cost, wherein it is possible to exclude mechanical control elements, and which can be used in high-speed Diesel engines.